This invention relates to a semiconductor laser device and more particularly to a stripe geometry buried double heterojunction structure semiconductor laser and its manufacturing method.
One advantage of what is conventionally referred to as a stripe-geometry buried double-hetero junction structure semiconductor laser is that, even with a small stripe width (1 to 2 .mu.m), it confines carriers and light as effectively in a direction parallel to the hetero junction interface as in a direction vertical to the heterojunction interface.
Therefore the expansion of the oscillation region is nearly equal in a direction either parallel or vertical to the junction interface, thereby achieving a point-like laser emission pattern at the output facets wherein laser beams are radiated substantially symmetrically with respect to the direction of the light propagation. Such a point laser beam can be focused by a conventional convex lens to a point with a size of its wavelength, and therefore it is suitable for use as the light source for video disks and optical fiber communications. Using a similar convex lens, the beam can also easily be converted into parallel beams forming a circular cross section, thus replacing a gas laser for potential use in many applications. However, since a buried heterostructure semiconductor laser as a point light source has transverse mode width as small as 1 .mu.m, such laser, especially one of GaAs/AlGaAs system, owing to the well known effect of catastrophic optical damage on mirrors, has its oscillation output limited to about 1 mW when oscillated continuously at room temperature, with the result that it can be used in only a very limited field of applications. In addition, the conventional buried heterostructure of GaAs/AlGaAs system has been manufactured by first forming a double heterojunction structure through a liquid phase epitaxial growth from a Ga solution, then removing the structure out of the growth boat for performing mesa etching, and thereafter performing the second liquid phase epitaxy. The second crystal growth occurs in the presence of a semiconductor whose surface has been oxidized with atmosphere after mesa etching, and therefore, defects will easily develop at the interface between the layer of the first grown semiconductor and that of the next grown semiconductor, thus providing a semiconductor device of short life time and low reliability. What is more, the second liquid phase growth has been a bottleneck in large-scale production because it requires a sophisticated technique so that a very tiny 1 .mu.m wide flat-topped mountain or "mesa" produced by mesa etching is not lost by meltback.